I. Field of the Invention
The present invention relates to turbine blades and, more particularly, to transpiration cooled turbine blades.
II. Description of the Prior Art
Presently known transpiration cooled turbine blades are formed with a porous wall defining a hollow interior. U.S. Pat. No. 3,619,082 (Meginnes) and U.S. Pat. No. 3,647,316 (Moskowitz) provide examples of such blades. The porous wall is formed of a plurality of layers bonded together so that the pores or holes in adjacent layers may be out of registration in order to provide for lateral movement of coolant fluid, as well as providing for the movement of such fluid from the interior of the blade to the surface. The coolant fluid is usually compressed air which enters from the blade base.
However, the presence of the various layers in the blades of the art can tend to restrict the rate of flow of coolant through the wall and the rate of passage of coolant to the edges of the blade. This prevents adequate and controlled cooling of the edges and surfaces and leads to stresses because of temperature differences from one part of the blade to another. Furthermore, when highly loaded, these blades may have a relatively high performance loss because the stream line over the low pressure exterior surface of the blade tends to separate from the surface of the blade to form eddy currents near the trailing edge of the blade. This reduces the power derived from each such blade.
There is therefore a need for a lightweight, relatively inexpensive transpiration cooled turbine blade, wherein loadings may be high without attendant performance losses and cooling of the blade edges and surface is effective and uniform.